The water that is used for homes, businesses, and agriculture in the San Pedro River Basin is the same source of water that keeps the San Pedro River flowing and its habitat healthy. All of the water that local communities use is pumped out of the underground aquifer. This same “groundwater” also seeps into the river, and keeps it flowing during periods when there is no rain.
If the amount of groundwater declines over time, it impacts both the ability of wells to supply water for human uses, as well as the flows in the San Pedro River. Long periods of drought can increase the chances for groundwater declines.
The U.S. Geological Survey (USGS) provides helpful information about groundwater on its USGS Water Science School website. The following two graphics and explanations from the USGS website are helpful in understanding how the underground aquifer interacts with the San Pedro River.
Natural Conditions: Water is recharged to the groundwater system by percolation of water from precipitation and then flows to the stream through the groundwater system.
Water-level declines: Water pumped from the groundwater system causes the water table to lower and alters the direction of groundwater movement. Some water that flowed to the stream no longer does so and some water may be drawn in from the stream into the groundwater system, thereby reducing the amount of streamflow.
The following USGS publications offer a deeper dive about groundwater and water availability in the Western U.S.:
- Groundwater and Surfacewater-A single resource- USGS Circular 1139
- Water Availability for the Western United States-Key scientific challenges- USGS Circular 1261
The CCRN recharge projects are constructed facilities located along 25 miles of the San Pedro River. These projects will help nature replenish groundwater by storing more stormwater and treated effluent back underground in the locations where it can benefit the flows of the river the most and help to ensure that the river will flow far into the future. The CCRN project sites have also reduced the potential for future groundwater pumping in the most sensitive locations, where pumping would have the most impact on the river. Permanent conservation easements have been placed on most of the project sites that will provide permanent legal restrictions against high volume pumping and large-scale developments in these areas.
The best available science using hydrologic monitoring and inventories, and predictive models, together with engineering studies, have informed both these recharge and conservation measures to ensure that the most effective and feasible projects are implemented to best meet regional water needs. The Upper San Pedro Partnership website provides access to many of these studies and reports.